The present invention relates to the field of dispensing machines intended to dispense and/or meter more or less viscous fluid products, such as for example paints, colorants, inks, and the like.
Prior art in the above sector comprises dispensing machines that run according to various operating principles. One fairly widespread type of known machine comprises multiple reservoirs for colorant fluids, connected to a dispensing circuit. Each fluid product is drawn from its respective reservoir by a positive-displacement pump and delivered to a corresponding three-way two-position distributing valve. When the valve is in an inactive position, the fluid is returned to its respective reservoir through a recirculation duct. When it is necessary to dispense a pre-set amount of fluid, the valve is set to an active position so as to deliver the fluid from the reservoir to a dispensing nozzle. This type of machine provides excellent results in terms of precision repeatability and reliability Of results over time. However, the use of a pump and solenoid valve for each reservoir of fluid product raises the overall cost of the machine, in terms of both manufacture and servicing. Another known type of dispensing machine for fluid products, especially colorant fluids, comprises a series of reservoirs connected to or integrated with syringe-type dispensing pumps, comprising plungers axially movable inside respective cylinders, the pumps being usually arranged around the circumference of a rotating drum. To distribute a pre-set amount of fluid product into a container, it is necessary to rotate the drum until the appropriate syringe is aligned with the container. Generally, therefore, in machines of this known type it is impossible to dispense multiple fluid products simultaneously into the same container, which leads to low productivity for machines of this known type. Various solutions have been proposed to overcome the above problem all fairly complicated and costly to manufacture and service. In addition, one intrinsic problem with known syringe-type machines lies in the difficulty of providing sufficient sliding seals between the plungers and cylinders to ensure good precision and repeatability over time in dispensing and metering. Also, use of these machines with aggressive or abrasive fluids leads to rapid wear on the sliding seals and thus a decline in the machine performance, which can only partly be overcome by constant servicing, which heavily increases the running costs of the machine.
The object of the present invention is to overcome the above problems with the prior art by providing a dispensing machine to dispense and/or meter fluid products which is easy and economical to manufacture and service, and which provides high precision and reliability over time, even when using aggressive, corrosive or abrasive fluid products. Another object of the present invention is to provide a machine that is compact in size with satisfactory productivity performance, especiallyxe2x80x94but not exclusivelyxe2x80x94when dispensing limited amounts of fluid products. A further object of the present invention is to provide a machine comprising a plurality of independent dispensing units which are easy to manufacture and install on the machine and which can be quickly replaced if needed, even by unskilled personnel, for example even the machine user. In order to achieve the above objects, the present invention relates to a dispensing unit having the characteristics described below. The invention also relates to a dispensing machine to dispense and/or meter fluid products, comprising a plurality of dispensing units of the above type.
According to a particular feature of the present invention, the dispensing unit comprises a pumping chamber with flexible walls, in particular but not exclusively bellows-like walls. In one particular embodiment, the pumping chamber is activated by a linear actuator in order to provide a linear proportion between the actuator stroke and the amount of product dispensed. According to a further particular feature, the linear actuator comprises a stepper motor to provide a linear proportion between the number of motor steps and the amount of fluid dispensed. Another special feature lies in the fact that, with the dispensing unit of the present invention, the pressure in the delivery duct to the dispensing nozzle drops immediately as soon as dispensing is interrupted, which prevents dripping and droplets at the nozzle.
According to another feature of the invention, the dispensing unit is set to filling position at the end of each dispensing, making the dispensing unit immediately available for the next delivery.
Yet another feature of the invention is that the dispensing unit comprises an optic limit sensor, which defines the zero point for the pumping unit. This feature makes it possible to achieve high repeatability of the dispensing process of a fluid product by the dispensing unit.
Another feature of the dispensing unit lies in the fact that the intake and dispensing strokes may take place at different speeds, to improve the machine productivity by reducing the time needed to refill the pumping chamber, yet without sacrificing precision during the dispensing phase.